cvs commit: src/sys/dev/uart uart_core.c

Marcel Moolenaar xcllnt at
Wed Mar 28 21:53:30 UTC 2007

On Mar 28, 2007, at 2:19 PM, Ben Kaduk wrote:

> On 3/28/07, Marcel Moolenaar <marcel at> wrote:
>> marcel      2007-03-28 18:26:12 UTC
>>   FreeBSD src repository
>>   Modified files:
>>     sys/dev/uart         uart_core.c
>>   Log:
>>   When we match UARTs found during bus-enumeration with UARTs used  
>> for
>>   system devices (i.e. console, debug port or keyboard), don't stop
>>   after the first match. Find them all and keep track of the last.
>>   The reason for this change is that the low-level console is always
>>   added to the list of system devices first, with other devices added
>>   later. Since new devices are added to the list at the head, we have
>>   the console always at the end. When a debug port is using the same
>>   UART as the console, we would previously mark the "newbus" UART as
>>   a debug port instead of as a console. This would later result in a
>>   panic because no "newbus" device was associated with the console.
>>   By matching all possible system devices we would mark the "newbus"
>>   UART as a console and not as a debug port.
>>   While it is arguably better to be able to mark a "newbus" UART as
>>   both console and debug port, this fix is lightweight and allows
>>   a single UART to be used as the console as well as a debug port
>>   with only the aesthetic bug of not telling the user about it also
>>   being a debug port.
> I am rather ignorant about such things, but is there any security risk
> in having an "undocumented" debug port?

There's no security issue. The user/administrator has to configure
the machine and/or kernel before there will be a UART-based debug
port. The kernel will announce when uart is used as a debug port.
There's just a particular case when the uart port in question will
not announce that it's the debug port.

Marcel Moolenaar
xcllnt at

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